1. Field of the Invention
The present invention relates to a projector apparatus, and more particularly relates to a holding mechanism of an image forming optical system.
2. Description of the Related Art
A large number of projector apparatuses using an aspherical reflecting mirror in place of a projection lens have been used recently. There have conventionally been strict requirements for the precision of the distance between a display device such as a liquid crystal display device and a reflecting mirror, and the precisions of the distances between a plurality of reflecting mirrors. To meet these requirements, these distance precisions are maintained by increasing the precisions of respective parts constructing the projector apparatuses, and consequently the precision of the projector apparatuses is managed.
However, the structure of the conventional projector apparatus is not prepared for a temperature change due to heat generated by a heat generation source such as a lamp, and this temperature change is addressed by cooling the housing itself, and thus, reducing the temperature change of the overall projector apparatus, for example.
Description will now be given of a fundamental construction of the conventional projector apparatus with reference to FIG. 1. As shown in FIG. 1, reflecting mirrors 1 to 3 are fixed to plate 6 respectively through holding members 1a to 3a. The projector apparatus shown in FIG. 1 is also comprised of a fourth reflecting mirror upon which light reflected by reflecting mirror 3 falls, and the fourth reflecting mirror is also fixed to plate 6 through a holding member, not shown (for example, see Japanese Patent Laid-open Publication No. 55306/2002). In this projector apparatus, the respective component parts expand by heat under various conditions such as an ambient temperature change during the operation, an internal temperature increase due to heat generated by lamp 8, and a temperature increase due to an optical power, and consequently, distortions occur in plate 6, holding members 1a to 3a, the unillustrated holding member holding the fourth reflecting mirror, and the like. If the distances between reflecting mirrors excessively change as a result of these generated distortions, the quality of a projected image degrades, and the performance of the apparatus thus decreases.
As a cross sectional view in FIG. 2 shows, plate 6 is fixed to housing 9 using screws 15. Housing 9 is made of magnesium, and plate 6 is made of a material having a low coefficient of linear expansion. Thus, as shown in FIG. 1, when radiant heat {circle around (1)} from lamp 8 heats housing 9, a linear expansion occurs at location {circle around (2)}, and forces expanding housing 9 in directions {circle around (3)} are generated, plate 6 warps in direction {circle around (4)}. In this state, it is not possible to maintain the quality of the projected image.